The present patent application concerns a two-component system, particularly for forming an adhesive, which is suitable, for example, for applications in the foundry industry and/or in the construction industry.
In the foundry industry, adhesive bonds between parts of foundry molds are presently often produced using organic hotmelt adhesives or polyurethane adhesives (in the form of two-component systems) or thermally curing inorganic waterglass adhesives.
Hotmelt adhesives, whose bonding effect is brought about through solidification of a melt, have to be melted before being used. This entails a relatively high cost in terms of apparatus and of time.
Organic adhesives are a disadvantage in the foundry industry, since at the high temperatures to which casting molds and casting cores are exposed, they give off volatile organic compounds (VOCs) and hence may give rise to defects (gas bubbles) in the fabricated casting.
In order to lower the emission of volatile organic compounds (VOCs) in foundries, therefore, mold materials with inorganic binders are increasingly being used for producing molds and cores. In this context it is desirable also to use adhesives which do not give rise to emissions of volatile organic compounds, or do so only to a small extent. Moreover, the compatibility between organic adhesives and mold materials bound by an inorganic binder, in terms of the materials involved, is often not very high, to the detriment of the reliability of the adhesive bonds.
The problems caused by the use of organic adhesives can be avoided if they are replaced by inorganic adhesives such as thermosetting waterglass adhesives. Thermosetting of waterglass-based adhesives, however, requires the removal of water, i.e., drying at elevated temperature, in an oven or a microwave heater, for example. This entails a relatively high cost in terms of apparatus and time. Moreover, there is a risk of incomplete curing of the waterglass, so making the resultant adhesive bonds sensitive to changes in atmospheric humidity.
Also known, besides the thermal curing of waterglass by removal of water, is the chemical curing of waterglass by means of carbon dioxide or by means of esters as curing agents.
EP 0 641 748 A1 discloses a composition for fastening plugs, threaded rods, and the like in cavities, especially drilled holes, in concrete, masonry, and brickwork, based upon waterglass with at least one fine-particle, high-activity coreactant such as SiO2 and/or AI2O3, for example, and also with fillers, such as finely ground quartz and/or silica sand, for example, where the waterglass has a molar ratio of SiO2 to alkali metal oxide of >1.4, preferably 1.45 to 1.60, but <2, and the composition further comprises, based on 100 parts by weight of waterglass, 10 to 40 parts by weight of a curing agent which neutralizes the alkali metal of the waterglass with elimination of an acid which is stronger than silicic acid. In the method for producing a composition of this kind, the waterglass is introduced initially (optionally together with a liquefying agent), the high-activity coreactants (such as SiO2 and/or AI2O3, for example) are added with stirring, and then, likewise with stirring, the fillers are added, and subsequently, at a high stirring speed, the curing agent is added. The compositions produced accordingly have pot lives of 25 minutes up to one hour and obtain their ultimate strength after 30 hours or more.